FDB motor with tapered shaft for improved pumping efficiency

ABSTRACT

For motors having a journal with one or more groove regions and a shaft for relative rotation in the journal, aspects include providing a dual tapered shaft. The shaft may be tapered by the application of a wear resistant coating at least opposite the groove regions. The coating introduces a shaft taper from near a top end and from near a bottom end towards the shaft middle. The shaft taper may provide for improved pumping efficiency. The coating may be applied in various processes such as chemical vapor deposition or physical vapor deposition to establish a thickness gradient of coating material from near the top end and near the bottom end towards the shaft middle. In one example, the coating includes a DLC coating. Additionally, shaft portions may be shielded to prevent coatings thereon.

RELATED APPLICATION

This application is related to and claims benefit of priority from U.S.Provisional Patent Application No. 60/554,961, filed on Mar. 19, 2004,and which is fully incorporated by reference herein as if fully setforth herein.

BACKGROUND

The present invention relates to grooved regions, such as pumping sealregions, in Fluid Dynamic Bearing (FDB) motors, and more particularly toincreasing pumping efficiency and/or reducing component wear neargrooved regions of FDB motors.

DESCRIPTION OF RELATED ART

Groove regions, such as grooved pumping seal regions, have been used inFDB motors. Some such FDB motors have a predominantly straight journalbearing formed by opposing inner and outer surfaces of relativelyrotating components. By example, a journal bearing may be formed betweenan inner surface of a bearing sleeve and an outer surface of a shaft.Such journal bearings are designed to maintain a gap between the innerand outer surfaces. Lubricating liquid may be disposed in the gap.

Grooved regions, such as grooved pumping seal regions, are typicallydisposed at one or both ends of the relatively rotating components. Thegrooved regions may be for pumping lubricating liquid away from openingsfrom which lubricating liquid may escape and/or evaporate. The groovedregions may also be for establishing a minimum flow of lubricatingliquid within portions of the motor. Grooved regions may tend toevacuate lubricating liquid from a portion of the journal, and thereforethere is some danger that the relatively rotating components may contacteach other if jolted or jarred during operation (op shock event). Thatcontact may induce wear in the components and may increase risk ofpremature drive failure.

SUMMARY

In exemplary aspects, a shaft for an FEDB motor comprises an elongatemember having an outer radial surface extending from a first end to asecond end and a coating disposed on the outer radial surface of themember. In one example the shaft is tapered from relatively widediameters at the first and second ends of the shaft to a relativelynarrow diameter between the first and second ends of the shaft. A shafthaving such dual tapered regions may increase the pumping efficiency ofa fluid dynamic bearing within an FDB motor.

In one example, the taper is achieved through the application of a wearresistant coating. The coating may be disposed from near the first endand extending towards a middle of the member. The coating may further bedisposed from near the second end and extending towards the middle ofthe member. The coating is provided with greater thickness near thefirst end and the second end than near the middle of the member. Thecoating may be a DLC coating, a ceramic coating, or some other wearresistant coating depositable through suitable processes such aschemical vapor deposition processes and physical vapor depositionprocesses.

The outer radial surface may be substantially cylindrical in the absenceof the coating disposed thereon, and after disposition of the coating,the coated outer radial surface may taper in diameter from the first endtowards the middle of the member and from the second end towards themiddle of the member. Portions of the shaft, such as a first end faceand a second end face may be maintained substantially free of thecoating.

The coating may be disposed on outer radial surface by providing firstcoating material from the first end directed obliquely at the outerradial surface and by providing second coating material from the secondend directed obliquely at the outer radial surface.

Other exemplary aspects include a motor that comprises a bearing sleevewith a journal. The journal has a top end, a bottom end, first groovesdisposed on an interior surface of the journal, and second groovesdisposed on the interior surface. The motor further comprises a shaftdisposed in the journal. The shaft comprises an elongate member having afirst end, a second end, and an outer radial surface. A first coatingmay be formed at least on a portion of the outer radial surface opposingthe first grooves. The first coating may taper in thickness from thefirst end of the member towards the second end of the member. A secondcoating may also be formed on the outer radial surface at least on aportion of the outer radial surface opposing the second grooves. Thesecond coating may taper in thickness from the second end of the membertowards the first end of the member.

Methods for forming coatings on relatively rotatable motor membersaccording to aspects of the invention may include providing an elongatemember symmetric about at least one axis of rotation. The member mayhave a first end, a second end, and an outer radial surface extendingfrom the first end to the second end. The methods may further compriseforming a first coating on the outer radial surface, where the firstcoating tapers in thickness from near the first end towards the secondend, and forming a second coating on the outer radial surface, where thesecond coating tapers in thickness from near the second end towards thefirst end.

BRIEF DESCRIPTION OF THE DRAWINGS

For describing aspects and examples herein, reference is made to theaccompanying drawings in the following description.

FIG. 1 illustrates a plan view of an exemplary disc drive;

FIG. 2 illustrates a cross-section of a motor having a shaft relativelyrotatable with respect to a journal of a bearing sleeve;

FIG. 3 schematically illustrates a vertical cross-section of the shaft;

FIGS. 4 a-d schematically illustrate various portions of the coatedshaft; and

FIG. 5 illustrates exemplary steps of a method for forming coatings onthe shaft.

DETAILED DESCRIPTION

The following description is presented to enable a person of ordinaryskill in the art to make and use various aspects of the inventions.Descriptions of specific materials, techniques, and applications areprovided only as examples. Various modifications to the examplesdescribed herein will be readily apparent to those skilled in the art,and the general principles defined herein may be applied to otherexamples and applications without departing from the spirit and scope ofthe inventions. For example, aspects and examples may be employed in avariety of motors, including motors for use in disc storage drives.Motors for disc storage drives may be designed and may operate in anumber of ways. Exemplary subject matter provided herein is forillustrating various inventive aspects and is not intended to limit therange of motors and devices in which in such subject matter may beapplied.

Turning briefly to FIG. 1, a plan view of an exemplary magnetic discdrive storage system is illustrated. In this example, the storage system10 includes a housing base 12 having spindle motor 14 that rotatablycarries storage discs 16. An armature assembly 18 moves transducers 20across the surface of the discs 16. The environment in which discs 16rotate may be sealed by seal 22 and cover 24. In operation, discs 16rotate at high speed while transducers 20 are positioned at any one of aradially differentiated track on the surface of the discs 16. Thisallows transducers 20 to read and write magnetically encoded informationon the surfaces of discs 16 at selected locations. Discs 16 may rotateat many thousands of RPM.

To produce rotation of discs 16, spindle motor 14 typically includes atleast one rotatable portion. The at least one rotatable portion is inturn typically supported by one or more bearing surfaces providing a lowfriction interface with a relatively non-rotating surface. In someexemplary motors, a shaft may rotate within a journal of a fixed bearingsleeve while in others the shaft may be stationary and the bearingsleeve may rotate about the shaft. Aspects described herein may be usedin any such motor types, even where described with reference to only oneof these motor types.

Turning now to FIG. 2, a cross-section of an exemplary spindle motor 14is illustrated. Motor 14 includes a bearing sleeve 205 with a journal210 defined by an interior surface (not separately indicated). Asillustrated, exemplary journal 210 extends from a top 206 of bearingsleeve 205 to a bottom 207 of bearing sleeve 205. Journal 210 includesgroove region 215 and groove region 216 disposed circumferentially onthe interior surface that defines journal 210. Groove region 215 and/orgroove region 216 may be asymmetrical and may function as pumping sealsand/or to recirculate lubricating liquid through portions of motor 14. Ashaft 220 is disposed within journal 210. Shaft 220 includes an outerradial surface 221 (illustrated in FIG. 3) that radially opposes theinterior surface of journal 210, thereby forming a gap (not separatelyindicated) where a hydrodynamic bearing region provides for low frictionrotation of shaft 220 in journal 210. The gap between the interiorsurface and shaft 220 may vary in size and shape amongst motor designs.

Shaft 220 may generally be an elongate member with outer radial surface221 extending from a first end 222 to a second end 224. In some aspects,shaft 220 may be approximately cylindrical, and first end 222 may havean approximately circular first end surface 225. Likewise, second end224 may have an approximately circular second end surface 226. Ifdesirable, shaft 220 may be crowned or conical (e.g., having a largerdiameter at one end) for a journal of a corresponding shape.

First end 222 of shaft 220, first coating region 235 is identified inFIG. 2 by demarcating (by beginning and ending arrows) a portion ofouter radial surface 221 having first coating region 235. In aspects,coating region 235 extends along outer radial surface 221 at least whereouter radial surface 221 opposes groove region 215 (i.e., coating region235 is at least disposed radially opposite groove region 215). Coatingregion 235 may be also be additionally disposed more proximate first end222 and more proximate second end 224. In some aspects, coating region235 extends approximately to but not entirely to first end 222;additionally first end surface 225 may be left uncoated.

Like coating region 235, second coating region 240 extends along outerradial surface 221 at least where outer radial surface 221 opposesgroove region 216 (i.e., coating region 240 is at least disposedradially opposite groove region 216). As further illustrated, coatingregion 240 may be more extensively disposed towards both first end 222and second end 224. In aspects, coating region 240 extends approximatelyto second end 224, but not entirely to second end 224. In some aspects,second end surface 226 is left uncoated. Aspects of shaft 220, coatingregion 235, and coating region 240 are further described with regard toFIG. 3.

FIG. 3 illustrates an exemplary schematic vertical cross-section ofshaft 220. This exemplary cross-section is not drawn to scale so thataspects may be better illustrated. As described above, shaft 220includes first end 222 and second end 224. Outer radial surface 221extends from first end 222 to second end 224 (and vice versa).

Coating region 235 may be disposed on outer radial surface 221 proximatefirst end 222. As illustrated and described above, a portion 302 ofouter radial surface 221 closer to first end 222 than coating region 235may remain uncoated. Exemplary coating region 235 is generally thickermore proximate than distal first end 222 (i.e., coating region 235becomes thinner closer to second end 224). In aspects, coating 235 maytaper monotonically from near first end 222 towards second end 224. Amaximum thickness of coating 235 may vary amongst designs. A thicknessof coating region 235 near a middle portion 309 of outer radial surface221 may be negligible or non-existent compared with a size of the gap inmiddle portion 309 (i.e., the coating may be very thin or non-existent).Middle portion 309 may be covered to prevent a coating from being formedthereon. Coating region 235 may terminate abruptly near first end 222,as illustrated by shoulder 305. Coating region 235 may be considered tohave a shape approximating a three-dimensional conical annulus (ifconsidered separately from outer radial surface 221 of shaft 220, uponwhich coating region 235 is applied).

Like coating region 235, coating region 240 may be disposed on outerradial surface 221, except that coating 240 may be disposed near secondend 224. A portion 303 of outer radial surface 221 closer to second end224 than coating region 240 may remain uncoated. Exemplary coatingregion 240 is generally thicker more proximate than distal second end224 (i.e., coating region 240 becomes thinner closer to first end 222).In aspects, coating 240 may taper monotonically from near second end 224towards first end 222. A maximum thickness of coating 240 may varyamongst designs. A thickness near the middle portion 309 of outer radialsurface 220 may be negligible or non-existent compared with a size ofthe gap in middle portion 309. Coating region 235 may terminate abruptlynear second end 224, such that coating region 240 may have a shapeapproximating a conical annulus (if considered separately from outerradial surface 221 of shaft 220, upon which coating region 235 isapplied).

Exemplary cross-sections of shaft 220 and coating region 235 disposedthereon are illustrated in FIGS. 4 a-d. FIGS. 4 a-d are not drawn toscale, but instead are drawn for illustrating various aspects discussedbelow. FIG. 4 a illustrates a portion of shaft 220 proximate first end222 and substantially without coating. In aspects, coating region 235and coating region 240 may be disposed to make shaft 220 approximatelysymmetric about a center of the shaft. (i.e., thicknesses of eachcoating region may be approximately circumferentially equal atequivalent distances from respective ends of the shaft). Coating region235 may also be radially symmetric in thickness at a given distance fromfirst end 222 (and likewise for coating region 240 from second end 224).

FIG. 4 b illustrates a thicker portion of coating region 235, designatedas shoulder 305 in FIG. 3 (and may also illustrate a thicker portion ofcoating region 240, at shoulder 310 in FIG. 3). In FIG. 4 b, theapproximately annular shape of each cross-section of coating region 235and of coating region 240 is evident upon recognizing shaft 220, aboutwhich coating region 235 and coating region 240 are disposed.

FIG. 4 c illustrates a central portion of coating region 235, designatedat 307 in FIG. 3. As illustrated, the coating thickness at 307 isthinner than the thickness at 305 illustrated in FIG. 4 b. FIG. 4 dillustrates a thinner portion of coating region 235 near the shaftmiddle 309 (approximately designated). As illustrated, a thickness ofcoating region 235 at 309 begins to be negligible compared with theradius (diameter) of shaft 220. As discussed above, middle portion 309may be shielded during coating deposition so as to keep middle portion309 substantially free from coating. FIGS. 4 c and 4 d may alsoillustrate corresponding portions of coating region 240, as one ofordinary skill in the art would comprehend.

Coating region 235 and coating region 240 may be comprised of suitablecoating material deposited on outer radial surface 221 (and on alreadydeposited coating material as the coating regions increase inthickness). Low-temperature chemical and/or vapor deposition processes,and other deposition processes may be used to provide the coatingmaterial.

Coating material may include any variety of diamond like coatingmaterials and ceramic type materials. In aspects, coating region 235 andcoating region 240 may comprise multiple separate coatings, where eachseparate coating may be of, or include, a different material. Byexample, a first layer of coating region 235 may be a layer designed toimprove adhesion of a later disposed carbon rich layer to outer radialsurface 221. Coating material may also be disposed in numerous coatings,depending on a desired coating thickness and devices used in forming thecoating (e.g., some machines may be limited in growth rate per time, orthe shaft 220 may be examined during coating deposition).

In exemplary aspects, coating region 235 and coating region 240 may beapproximately 0.5-3.0 μm thick at their thickest respective points andtaper uniformly towards shaft middle 309. In exemplary aspects, nearshaft middle 309 coating region 235 and/or coating region 240 may be ofnegligible thickness, for example, less than 0.5 μm, and in someexamples may not coat the entirety of outer radial surface 221 nearshaft middle 309 (i.e., coating material may be disposed near shaftmiddle 309, but the coating material may not form a continuous coatingregion). For other background relating to coatings, refer to U.S. Pat.No. 6,664,685, entitled, “HIGH ADHESION, WEAR RESISTANT COATINGS FORSPINDLE MOTORS IN DISK DRIVE/STORAGE APPLICATIONS,” filed on Dec. 13,2001, which is incorporated in its entirety by reference.

Devices for carrying out such processes are disposed to cause coatingmaterial to be provided about outer radial surface 221. In aspects,while forming coating region 235, the coating material may be providedfor greater thickness near first end 222 than towards second end 224,and at approximately constant thickness circumferentially around outerradial surface 221 at a given distance from first end 222. Coatingregion 240 may be formed under respective similar conditions.

An exemplary way to establish the coating material thickness describedabove is to provide the coating material from near first end 222 forestablishing coating region 235. Likewise, for establishing coatingregion 240, coating material may be provided from near second end 224.In so doing, a desired differential in thickness may be establishedthrough diffusion along outer radial surface 221 from a source ofcoating material. One aspect that may be understood by one of skill inthe art is that the surface coated (outer radial surface 221) liessubstantially parallel to a source direction of coating material. Bycontrast, generally surfaces coated with DLC material or the like arecoated by material provided from a direction substantially perpendicularto the surface to be coated. Advantageously, providing coating materialin such a manner more easily establishes a desirable taper shape foreach of coating region 235 and coating region 240.

FIG. 5 illustrates exemplary steps of a method for forming coatingregion 235 and coating region 240 on shaft 220. Step 505 includesshielding first end surface 225 and second end surface 226; theshielding may extend along portion(s) of outer radial surface 221 nearrespective first end 222 and/or second end 224. An amount of outerradial surface 221 covered may compensate for shadow effects caused bythe shielding such that coating region 235 substantially begins at adesired point on outer radial surface 221 (e.g., shoulder 305 in FIG. 3)and at an appropriate thickness (as selected for a specific design). Ofcourse, one or both of first end surface 225 and second end surface 226may be covered to prevent coating formation thereon, if desired for aparticular application.

Step 510 includes relatively disposing a first source of material andshaft 220 so that one of first end surface 225 and second end surface226 opposes the first source of coating material. Step 515 includesbeginning to emit coating material from the first source into a regionsurrounding outer radial surface 221 (i.e., into the immediate volumearound shaft 220). Step 520 includes ceasing to emit coating materialfrom the first source after a predetermined amount of time has elapsed.Step 525 includes redisposing shaft 220 so that the other of the firstend surface 225 and the second end surface 226 (the one disposed distalthe source at 510) faces the first source. Step 530 includes beginningto emit coating material from the first source. Step 535 includesceasing to emit coating material from the first source after thepredetermined amount of time has again elapsed.

First end surface 225 and second end surface 226 may each be disposedapproximately perpendicular to the source such that outer radial surfaceis approximately parallel to the source. In such relative dispositions,coating material may contact outer radial surface 221 obliquely. Firstend surface 225 and second end surface 226 may also be disposed at someangle to the source. By rotating shaft 220 frequently, an approximatelyuniform cross-sectional coating thickness may be established (i.e., eachcross-section has an approximately constant thickness about outer radialsurface 221. Other adjustments may be made as necessary to establish auniform coating growth rate at a given distance from the source alongouter radial surface 221.

In a variation on the method of FIG. 5, a second source of material maybe relatively disposed with shaft 220 to face the other of the first endsurface 225 and the second end surface 226. Further modifications mayinclude beginning to emit coating material from the second source instep 515, and ceasing to emit coating material from the second source instep 520 after the predetermined amount of time has elapsed. In such avariation, step 525 may be eliminated, since there may be no need toredispose shaft 220 as coating region 235 and coating region 240 may becreated together.

Other variations may include disposing shield near the middle portion309 of shaft 220. Still other variations may include shielding portionsof shaft 220 for a portion of the predetermined amount of time andexposing those portions for a remaining time. Further variations mayinclude emitting matter for different amounts of time from each sourceto establish asymmetrical coatings. Still further variations may includemeasuring coating thickness during deposition and ceasing provision ofmatter when a desired thickness has been achieved (in addition to or inplace of emitting coating material for the predetermined time).Deposition may also be conducted in numerous discrete time intervals,rather than providing matter for a single predetermined time. Shaft 220may be disposed on a stationary holder or a conveyor that moves parallelto the first and/or the second matter source. One of skill in the artwould understand that coating region 240 may be formed before, after, orsimultaneously with coating region 235. Other modifications andvariations may be apparent to one of skill in the art.

To summarize certain aspects of the invention, a thickness gradient ofcoating material may be established from first end 222 and extendingtowards middle portion 309. The thickness gradient would provide forrelatively large thickness near first end 222 and for decreasingthickness more distal first end 222. A similar thickness gradient may beestablished from second end 224 by either a separate source of coatingmaterial or by the same source after coating region 235 has been formed(or vice versa if coating region 240 were formed first).

Various motor and FDB aspects have been illustrated and describedherein. One of ordinary skill in the art would understand that teachingsrelated to each may be adapted to other designs. Also, it would beunderstood that certain components have been separately identifiedherein, but such identification does not imply that such components mustbe separately formed from other components. Similarly, componentsidentified herein may be subdivided into sub-components in otherdesigns. Additionally, illustrated features such as recirculationchannels, bearing surfaces, pumping grooves, and the like may bedisposed additionally or differently than presented in aspects herein.

Other modifications and variations would also be apparent to those ofordinary skill in the art from the exemplary aspects presented. Byexample, various exemplary methods and systems described herein may beused alone or in combination with various fluid dynamic bearing andcapillary seal systems and methods. Additionally, particular exampleshave been discussed and how these examples are thought to addresscertain disadvantages in related art. This discussion is not meant,however, to restrict the various examples to methods and/or systems thatactually address or solve those disadvantages.

1. A dual tapered shaft for a fluid dynamic motor, comprising: anelongate member having an outer radial surface extending from a firstend to a second end, wherein, a diameter of the outer radial surface istapered in thickness from proximate the first end towards the middle andtapered in thickness from proximate the second end towards the middle.2. The shaft of claim 1, wherein the elongate member includes a coatingat the outer radial surface, the coating disposed proximate the firstend and extending towards a middle of the member and further disposedproximate the second end and extending towards the middle of the member,the coating thicker proximate the first end and the second end thanproximate the middle.
 3. The shaft of claim 2, wherein the first endincludes a first end face and the second end includes a second end face,and the first end face and the second end face are substantially free ofthe coating.
 4. The shaft of claim 2, wherein the outer radial surfaceincludes a portion most proximate the first end substantially free ofthe coating, and a portion most proximate the second end substantiallyfree of the coating.
 5. The shaft of claim 2, wherein the coating at athickest point proximate the first end has a thickness approximatelybetween 0.5 μm and 3.0 μm, and at a thickest point proximate the secondend has a thickness approximately between 0.5 μm and 3.0 μm.
 6. Theshaft of claim 5, wherein the coating at the outer radial surfaceproximate the middle of the member is less than 0.5 μm.
 7. A motor,comprising: a bearing sleeve having a journal, the journal having a topend, a bottom end, first grooves disposed on an interior surface of thejournal, and second grooves disposed on the interior surface; and ashaft disposed in the journal, the shaft comprising: an elongate memberhaving a first end, a second end, and an outer radial surface, wherein adiameter of the outer radial surface is tapered in thickness fromproximate the first end towards the middle and tapered in thickness fromproximate the second end towards the middle.
 8. The motor of claim 7,wherein the shaft includes a cylindrical shaped member having a coatingthat varies in thickness.
 9. A method, comprising: providing an elongatemember symmetric about at least one axis of rotation, the member havinga first end, a second end, and an outer radial surface extending fromthe first end to the second end; forming a first coating on the outerradial surface, the first coating tapering in thickness from proximatethe first end towards the second end; and forming a second coating onthe outer radial surface, the second coating tapering in thickness fromproximate the second end towards the first end.
 10. The method of claim9, wherein the first coating has a negligible thickness proximate thesecond end and the second coating has a negligible thickness proximatethe first end.
 11. The method of claim 9, wherein the first coating hasat a thickest point proximate the first end a thickness approximatelybetween 0.5 μm and 3.0 μm, and the second coating has at a thickestpoint proximate the second end a thickness approximately between 0.5 μmand 3.0 μm.
 12. The method of claim 9, wherein the first coating isprovided from proximate the first end and obliquely directed towards theouter radial surface; and the second material is provided from proximatethe second end and obliquely directed towards the outer radial surface.13. The method of claim 9, further comprising: disposing the first endto oppose a source of coating material for forming the first coating;and disposing the second end to oppose the source of coating materialfor forming the second coating.
 14. The method of claim 13, furthercomprising: ceasing provision of the first coating material beforebeginning provision of the second coating material.
 15. The method ofclaim 9, further comprising shielding a portion of the outer radialsurface near the first end and a portion of the outer radial surfacenear the second end when forming the first and the second coating. 16.The method of claim 9, wherein the member provided is a substantiallycylindrical motor shaft.
 17. The method of claim 9, wherein the firstcoating and the second coating are sourced in one of the followingprocess types: chemical vapor deposition and physical vapor deposition.18. The method of claim 9, wherein the first coating and the secondcoating include diamond like coating material.
 19. A shaft manufacturedby the method of claim 9.